Ammonia reaction quotient

In this section, you learned that the expression for the reaction quotient is the same as the expression for the equilibrium constant. The concentrations that are used to solve these expressions may be different, however. When Qc is less than Kc, the reaction proceeds to form more products. When Qc is greater than Kc, the reaction proceeds to form more reactants. These changes continue until Qc is equal to Kc. Le Chatelier s principle describes this tendency of a chemical system to return to equilibrium after a change moves it from equilibrium. The industrial process for manufacturing ammonia illustrates how chemical engineers apply Le Chatelier s principle to provide the most economical yield of a valuable chemical product. 

A mixture of nitrogen, hydrogen and ammonia gases are in a sealed container and are at equilibrium. Which of the following changes will affect the reaction quotient (gc) but not affect the equilibrium constant (K )7... 

When the reactants and products of a given chemical reaction are mixed, it is useful to know whether the mixture is at equilibrium and, if it is not, in which direction the system will shift to reach equilibrium. If the concentration of one of the reactants or products is zero, the system will shift in the direction that produces the missing component. However, if all the initial concentrations are not zero, it is more difficult to determine the direction of the move toward equilibrium. To determine the shift in such cases, we use the reaction quotient (Q). The reaction quotient is obtained by applying the law of mass action, but using initial concentrations instead of equilibrium concentrations. For example, for the synthesis of ammonia,... 

To construct the reaction quotient for any reaction, write the balanced equation first. For the formation of ammonia from its elements, for example, the balanced equation (with colored coefficients for easy reference) is... 

He also found that the effect on the equilibrium concentration quotients of varying the ammonium nitrate concentration was extremely small the value of extrapolated to zero concentration of ammonium nitrate is 1.15 X 10 mole- P. Since the reactions are probably the successive replacement by ammonia molecules of two water molecules attached to a silver ion, the charge of the complex remaining unchanged, it is not surprising that changes of ionic environment have similar effects on the activity coefficients of the several ions. 

Nevertheless, either increasing the outlet ammonia concentration or reducing space velocity is confined by the equilibrium ammonia concentration. Where, the catalyst efficiency ( ex/ e) is defined as the ratio of outlet ammonia concentration ( ex) to equilibrium ammonia concentration (y e) under same conditions, which indicates the degree of the reaction close to the equilibrium. The efficiency of the present catalysts used in industry is about 90% at higher temperatures, as shown in Table 1.5. For example, the efficiency of ZA-5 catalyst is about 95% at about 475°C at the space velocity of 3 x 10 h and pressure of 15 MPa, which is very close to the equilibrium concentration of ammonia. With low space velocities, the operating temperature can be decreased as the outlet ammonia concentration is close to equilibrium concentration. As shown above, the efficiency of ZA-5 is about 98% at above 450°C and at the space velocity of 1 x 10 h Thus, it is impossible to further increase the outlet ammonia concentration under these conditions. As a result, the activity at low temperatures must be increased, since equilibrium ammonia concentration is higher at low temperatures. The outlet ammonia concentration is 16.68% on ZA-5 catalyst at 400°C and with the space velocity of 3 x 10 h and pressure of 15 MPa, the equilibrium concentration is 32.83%, and therefore the catalyst efficiency is only 50.8%. If the catalytic efficiency can be increased to more than 95% at 400°C by increasing the catalyst s activity at this temperature, the synthetic quotient per pass could be about 50%. 

---